The present invention relates in general to optical cables, and more particularly to an optical cable having a central cavity that provides a predetermined gap between (1) an inner diameter of an outer sheath and (2) an outer diameter of the contents within the cable""s central cavity. The gap prevents optical wave guides within the central cavity from being damaged upon opening the outer sheath.
Central cavity cables are known in which optical fibers (or soft buffer tubes containing optical fibers) are provided in a core tube that extends along the axis of the cable. An outer sheath, which may or may not include armoring, surrounds the core tube. Although core tube cable designs are generally thought to be acceptable, they are not without shortcomings. The shortcomings are most apparent when considering conventional, cable opening techniques. A cable may need to be opened, for example, to perform optical fiber splicing.
Cable opening involves penetrating through the outer sheath and the core tube in order to gain access to the optical fibers and soft buffer tubes. Two primary techniques are employed for removing the outer sheath. In the first technique, a user pulls on a ripcord that is interposed between the core tube and the outer sheath. When pulled with enough force, the ripcord cuts through the outer sheath. In the second technique, a user manipulates a cutting tool to penetrate through the outer sheath and partially into the core tube. That is, the cutting tool penetrates past the outer sheath""s inner diameter and partially into the wall thickness of the core tube. Once the outer sheath is removed, the core tube is then opened to gain access to the central cavity in which the optical fibers and soft buffer tubes are provided.
In both sheath removal techniques, the core tube shield""s the optical fibers from the ripcord and/or the cutting tool. That is, the core tube prevents the ripcord from passing through to the interior of the central cavity, and/or provides a cutting depth margin for the cutting tool. A special tool must be used to open the core tube, which is different from the cutting tool used to cut the sheath. Accordingly, gaining access to the cable""s central cavity is cumbersome and time consuming.
Moreover, some new cable designs do not include a core tube. These new designs are limited, however, because they remain difficult to open. For example, if the ripcord technique were employed, both the ripcord and the optical fibers would occupy the central cavity. When pulled, therefore, the ripcord could pass through the central cavity and damage the optical fibers. Similarly, if the cutting tool technique were employed, there would be no cutting depth margin to prevent/avoid optical fiber damage.
It is therefore an object of this invention to provide a cable having a predetermined gap that (1) protects the fibers and soft buffer tubes during tool access, (2) eliminates the need for a rigid core tube, and (3) improves the accessibility of the optical fibers.
The invention resides in a cable having an optical wave guide and a tape provided around the optical wave guide. The optical wave guide and the tape are provided in a central cavity of an outer sheath. The central cavity is sized to accommodate a predetermined gap between (1) the outer sheath and (2) the tape and the optical wave guide. During a cable opening process, the predetermined gap forms a void that serves as a cutting tool depth buffer. Preferably, the predetermined gap is at least 2.0 mm and more preferably at least 0.25 mm.
The above and other features of the invention including various and novel details of construction will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular cable embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.